The HMGU thoron experimental house: a new tool for exposure assessment.

A thoron experimental house was constructed in a laboratory room of Helmholtz Zentrum München to perform exposure studies of thoron and its decay products under controlled conditions. The single room house (7.1 m(3)) was built from unfired clay stones and clay plaster. For the plaster of the inner side, the clay was mixed with granite powder enriched with (232)Th. The thoron inventory increased by this means to about 1700 Bq and the progeny potential alpha energy to 130 µJ inside the room. The instrumentation of the experimental house includes active and passive devices for thoron and thoron decay product measurement including attached and unattached progeny, for aerosol particle number and size measurement and characterisation of the climatic conditions. Various parameters as ventilation rate and aerosol concentration can be adjusted. Experiments performed in the experimental house demonstrate the experimental power of this new tool for indoor thoron exposure assessment.